Electronic nicotine delivery systems (“ENDS”), often referred to as electronic cigarettes or e-cigarettes, are rapidly becoming a popular alternative to cigarette smoking worldwide. ENDS typically consist of a battery, heating component, and a cartridge or tank containing tobacco-derived nicotine in a solution composed of glycerin and/or propylene glycol (“PG”), and flavorings. Upon activation, the heating element heats the solution and the consumer inhales the resulting vapor. Two general types of ENDS exist in the market currently. The “cig-alikes” are similar in appearance to conventional cigarettes and are largely used in the form purchased. “VTMs” (vapors-tanks-mods) are typically larger in size, stronger and interchangeable batteries, and allow subjects to fill the device with solutions customized in flavor and nicotine concentration.
The inventors are unaware of any well-controlled studies published to date that have been able to attribute a specific level of PG exposure from the use of ENDS products. One limiting factor in this assessment is that PG is commonly consumed in foods and beverages, making it impossible to definitively differentiate PG exposure from multiple sources. To overcome this limitation, PG can be synthesized with a carbon-heavy atom (C13, non-radioactive stable isotope) and safely administered to subjects using commercial vaporizer products. Using LC/MS/MS methods, the resulting PG exposure can then be definitively linked to use of the device not only by those who use the product, but also by individuals who are exposed to the second-hand vapor.
PG is widely used in the pharmaceutical, cosmetic, and food industries as a preservative, solvent, and humectant, and is generally regarded as safe by the United States Food and Drug Administration. PG is metabolized in the liver by alcohol dehydrogenase to lactic acid and then pyruvate, and ultimately carbon dioxide and water, while approximately 45% is excreted by the kidneys unchanged or as the glucuronide conjugate. The half-life of PG is approximately 4 hours. The average daily intake of PG from food products in the US is estimated to be approximately 2400 mg. A wide variety of foods contain PG, including ice cream, cake mixes and frosting, cookies, candy, salad dressing and soft drinks.
Electronic nicotine delivery systems essentially eliminate the inhalation of combustion products of conventional cigarettes by providing a tobacco extract or similar material containing nicotine dissolved in a solvent, usually propylene glycol or glycerin. This material is then heated in the e-cigarette, typically by induction heating, which causes the solvent and nicotine to vaporize. The resulting vapor is then inhaled which delivers the nicotine to the user. In the process of heating the solvent some of the solvent is converted to formaldehyde and acetaldehyde, which is also inhaled.